This invention relates to soft-ware defined radios and, more specifically, software defined radios using tunable material for significant system improvements.
Following a modem trend in radio design whereby radios are becoming increasingly flexible and software definable, more processing is done in the digital domain and preferably, in software. Large chunks of the RF spectrum are digitized at once, enabling an open architecture with regards to RF waveforms.
In the current expanding wireless communication environment, systems require both high data rates and high processing gains. Wideband transceivers are essential to realize these features demanded by wireless communication systems. In fact, it is believed that the next generation of wireless transceivers, for both multimedia applications and for wireless networking, must be wideband systems.
In addition, a large variety of digital systems have recently emerged in the wireless market. To combine the emerging digital systems with existing analog systems, and to reduce the cost of a wireless system, a new technology, i.e., a wideband software-defined radio (SDR) base station system, is developing. Essentially, in a software-defined radio base station transmitter, digital base-band channels are processed separately. All channels are then combined together, and the combined signal (i.e., a wideband multiple channel signal), after a digital to analog conversion, is then up-converted to RF by a wideband multiple channel frequency converter.
The current performance of analog to digital converters (A/D's) and digital to analog converters allows instantaneous RF bands of 10–30 Megahertz to be handled with spurious free dynamic range (SFDR) not exceeding 100 dB and signal to noise ratio (SNR) not exceeding 75 dB. The instantaneous RF band can be (software) tuned anywhere up to about 200 MHz and even several GHz in experimental systems.
However, for a software-defined radio (SDR) to be truly flexible and interoperable, operation over the entire 30–2000 MHz band is required. Receive signal levels may be as low as −120 dBm and as high as 0 dBm in a hostile environment, demanding a 120 dB dynamic range. Furthermore, emissions from colocated transmitters could amount to 100 Watt at the SDR receiver antenna. Co-site interference would thus require a dynamic range of more than 170 dB.
Despite advances in converter technology bringing a doubling of instantaneous bandwidth and sampling frequency every few years, SDR in its pure form will not be a practical reality for quite some time. As had been the case with traditional radios since the invention of the super-heterodyne receiver almost a century ago, the analog RF front end is still looked upon to provide the required tuning, selectivity and interference rejection. Thus, there is a strong need in the RF industry and more particularly in the software-defined radio technology industry for a flexible and interoperable operation over a very wide bandwidth and to enable a dynamic range of more than 170 dB and solves the problem in radio communications of resolving (separating) friendly, wanted signals, from interfering or unwanted signals and noise.